1. Technical Field of the Invention
The present invention relates to a method for coating a sliding surface of a high-temperature member, the high-temperature member, and an electrode for an electro-discharge surface treatment.
2. Description of the Related Art
FIG. 1 is a schematic diagram of a shrouded turbine blade as an example of a high-temperature member seen from a shroud portion, and FIG. 2 is another perspective view of a shroud section.
The shrouded turbine blade is constituted of a blade portion 1, a dove tail portion 2, and a shroud portion 3. The blade portion 1 is a portion which has a blade-shaped section and in which a rotation power is generated by combustion gas. The dove tail portion 2 is positioned in a terminal end portion of the blade portion 1, and is fixed to a turbine disk (not shown) to transmit the rotation power to the turbine disk. The shroud portion 3 is attached to a blade tip end, and has a function of suppressing vibration or reducing a gas leakage in the tip end.
As shown in this figure, the shroud portions are formed to be integrated with one or a plurality of blade portions 1, and are assembled to closely contact with one another. The closely contact surface (abutment surface) is simply linear as seen from a radial direction in some case, and is stepped midway in the other case as in this example. The surface stepped midway will hereinafter be referred to as “Z-notched”.
For a Z-notched shroud portion, shroud portions disposed adjacent to each other as shown by a two-dot chain line in FIG. 1 abut on each other on side surfaces A, B of a Z notch 3a to hold the entire position. Therefore, the Z-notched shroud portions have characteristics that the portions have a high position hold capability without being connected to each other.
However, the turbine blade rotate at a high speed during operation, and not only undergoes periodic deformation and vibration but also is exposed to the combustion gas at a high temperature passed through the turbine blade. Therefore, there is a problem that the side surfaces A, B of the shroud portion receive a high surface pressure at the high temperature while rubbing, and are severely abraded. It is to be noted that the sliding surfaces A, B are not fixed, and one surface is defined as A while the surface abutting on the one surface is defined as B.
To solve the problem, a hard heat-resistant/wear-resistant metal has heretofore been build-up welded or thermally sprayed to the surfaces disposed adjacent to the Z notch of the turbine blade and sliding against each other (side surfaces A, B, hereinafter referred to as “sliding surfaces A, B”) (e.g., [Reference 1]).